Legionella is a genus of Gram-negative bacteria comprising many species and distinct antigenic types with Legionella pneumophila being the most common pathogenic species. Legionaires' disease is the common name for a variety of diseases resulting from infection by Legionella bacteria. The most common presentation of many Legionella species is acute pneumonia (legionellosis), but many species of the bacteria are also capable of causing an influenzalike illness known as Pontiac fever (Winn, W. C. Jr. (1996). Legionella (In: Baron's Medical Microbiology, Baron, S. et al., eds. (4th ed.). University of Texas Medical Branch).
Legionella species are widely present in environmental water supplies such as rivers, lakes, and drinking water. To prevent infection by these bacteria, water is often disinfected with chlorine or heat, but bacteria often remain following these treatments. Of particular concern are nosocomial infections by these bacteria, given that many hospital water supplies have been demonstrated to contain Legionella bacteria. Hospitals expend a large amount of resources on a variety of disinfectant methods to reduce Legionella infections (Yu V L, Infection Control and Hospital Epidemiology (2011) 32(2). Controlling Legionella in Hospital Drinking Water: An Evidence-Based Review of Disinfection Methods).
Other known environmental sources of Legionella bacteria include swimming pools, evaporative condensers, cooling towers, nebulizers, humidifiers, ornamental fountains, and whirlpool spas. Dissemination of bacteria from environment to host generally requires aerosolization of the contaminated water. The contaminated water in the aforementioned sources can be aerosolized incidentally, for example during toilet flushing, or by design, as seen in nebulizers and fountains. Inhalation of these bacterial aerosols is thought to lead to the acute pneumonia observed in patients exhibiting legionellosis.
Recognizing the public health concerns posed by Legionella bacteria, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) established a Standard Practice for use by facility managers and owners to prevent Legionella contamination in building water systems. This standard, known as ASHRAE Standard 188P, specifies a practice to identify the conditions in a water system that can be made less favorable to the growth and transmission of Legionella. To optimize the advice given in this report, Hazard Analysis and Critical Control Point (HACCP) plans were used.
What is needed are new systems for addressing public health risks associated with Legionella bacteria.